THE BEGINNINGS OF II FE. 257 



concentrated results of those very tendencies to assume 

 specific forms modifiable by circumstances, which we 

 see manifested by the organisms met with in infusions. 

 Had such tendencies been absent, the multitudinous 

 forms of living matter could never have attained their 

 present diversity and complexity. So that a belief in 

 the existence of inherent tendencies to assume specific 

 forms, in the lowest organisms, is as necessary for the 

 biologist as a belief in the '- Law of Heredity^ — whereby 

 the potentiality of assuming any acquired specific form, 

 however complex, is bequeathed to the germ of each 

 organism. 



In the case of the evolution of the ciliated infusorial 

 animalcule, we have no mysterious inherited poten- 

 tialities to fall back upon. The different nature of 

 the materials, and the different combinations of inci- 

 dent physical forces by which the changes are brought 

 about, are the only factors entering into the problem. 

 But the intimate nature of the living matter of which 

 the pellicle is composed, may be understood to vary 

 almost ad infinitum according to the nature and quantity 

 (relative and absolute) of the organic ingredients en- 

 tering into the composition of the infusions, and the 

 degree in which they have been modified by the action 

 of heat. And when we consider, how these varying 

 initial combinations may have been acted upon by 

 many difiPerent combinations of physical forces, both 

 during the evolution of the primary organic units and 

 also during the secondary or derivative origin of the 



VOL. II. s 



